Guarantees by SEO experts/agencies and service providers for assured “Number 1 position” in the Search Engine Result Page is a false claim. With Google updating its algorithms now and then, no SEO expert can control the search engine. So, there is no way to control and predict the ranks on the index page in the Search Engine.
At the very best, they can work on improving your product/category pages’ optimization and ranking. And you will get to see the difference for the better but there’s no such “no. 1 position” guarantee in Ecommerce SEO.